This invention relates generally to gas turbine combustion technology and, more specifically, to an impingement cooled metal shield located around the inside edge of a combustor component, for example, a combustion liner at the forward and aft edges of the air mixing holes formed in the liner.
In a gas turbine combustion system, the combustion chamber casing contains a liner which is typically of a tubular or annular configuration with a closed end and an opposite open end. Fuel is ordinarily introduced into the liner via one or more fuel nozzles at or near the closed end, while combustion air is admitted through circular rows of apertures or air mixing holes spaced axially along the liner. These gas turbine combustion liners usually operate at extremely high temperatures and depend to a large extent on incoming combustion air from an appropriate compressor for cooling purposes.
Cracking around combustion liner air mixing holes is a common life-limiting failure mode for gas turbine combustor liners. In this regard, certain gas turbine engines use highly reactive fuel as the primary fuel source. Highly reactive fuel tends to pull the flame forward in the liner and anchor the flame both before (upstream of) and after (downstream) mixing row holes, typically most pronounced on the first mixing hole row (i.e., at the end of the liner closest to the fuel nozzles). Additionally, low BTU fuels and subsequent higher volume fuel flow amplify these flame anchoring effects. Other typically used fuels, on the other hand, cause the flame to anchor after or downstream of the mixing holes. Nevertheless, tests have confirmed very high temperatures on both sides of the air mixing holes.
While the problem of cracking has been addressed for locations downstream of the air mixing holes where the flame normally anchors, cracking problems along the upstream edge of the air mixing holes have not been addressed.
Thus, current solutions involve reestablishing cooling film flow only along the downstream edge of the air mixing hole, the flow having been interrupted by the radial flow of air through the air mixing hole. Air mixing hole inserts, sometimes referred to as refilmers, have been used to reestablish a cooling flow film along the interior surface of the combustor liner downstream of the air mixing hole as exemplified, for example, in U.S. Pat. No. 4,622,821. Other refilmer devices are disclosed in U.S. Pat. Nos. 4,875,339; 4,653,279; and 4,700,544.